a) 99−97+95−93+...+7−5+3−199-97+95-93+...+7-5+3-1
=(99−97)+(97−93)+....+(7−5)+(3−1)=(99-97)+(97-93)+....+(7-5)+(3-1)
=2+2+....+2+2=2+2+....+2+2
Có : [(99−1):2+1]:2=25[(99−1):2+1]:2=25 cặp có giá trị =2=2
=2.25=2.25
=50
b) 189 + 424 + 511 + 276 + 55`
=(189+511)+(424+276)+55=(189+511)+(424+276)+55
=700+700+55=700+700+55
=1455
c) (125.37.32):4(125.37.32):4
=(125.37.8.4):4=(125.37.8.4):4
=125.8.37=125.8.37
=1000.37=1000.37
=37000
d) 36.28+28.63+64.141−64.4136.28+28.63+64.141-64.41
=28.(36+63)+64.(141−41)=28.(36+63)+64.(141-41)
=28.99+64.100=28.99+64.100
=28.(100−1)+6400=28.(100-1)+6400
=2800−28+6400=2800-28+6400
=9200−28=9172
e) 5+8+11+14+...+3025+8+11+14+...+302
=(302+5).[(302−5):3+1]2=(302+5).[(302-5):3+1]2
=307.1002=307.1002
=307.50=15 350
f) 7+11+15+19+...+2037+11+15+19+...+203
=(203+7).[(203−7):4+1]2=(203+7).[(203-7):4+1]2
=210.502=210.502
=210.25=210.25
=5250
